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Eukaryotic Cell, September 2008, p. 1487-1499, Vol. 7, No. 9
1535-9778/08/$08.00+0     doi:10.1128/EC.00193-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Nucleus-Specific Importin Alpha Proteins and Nucleoporins Regulate Protein Import and Nuclear Division in the Binucleate Tetrahymena thermophila{triangledown} ,{dagger}

Colin D. Malone,{ddagger} Katarzyna A. Falkowska, Alanna Y. Li, Sarah E. Galanti, Reshi C. Kanuru, Elizabeth G. LaMont, Kate C. Mazzarella, Alan J. Micev, Morwan M. Osman, Nicholas K. Piotrowski, Jason W. Suszko, Adam C. Timm, Ming-Ming Xu, Lucy Liu, and Douglas L. Chalker*

Biology Department, Washington University, St. Louis, Missouri 63130

Received 12 June 2008/ Accepted 20 July 2008

The ciliate Tetrahymena thermophila, having both germ line micronuclei and somatic macronuclei, must possess a specialized nucleocytoplasmic transport system to import proteins into the correct nucleus. To understand how Tetrahymena can target proteins to distinct nuclei, we first characterized FG repeat-containing nucleoporins and found that micro- and macronuclei utilize unique subsets of these proteins. This finding implicates these proteins in the differential permeability of the two nuclei and implies that nuclear pores with discrete specificities are assembled within a single cell. To identify the import machineries that interact with these different pores, we characterized the large families of karyopherin homologs encoded within the genome. Localization studies of 13 putative importin (imp) {alpha}- and 11 imp β-like proteins revealed that imp {alpha}-like proteins are nucleus specific—nine localized to the germ line micronucleus—but that most imp β-like proteins localized to both types of nuclei. These data suggest that micronucleus-specific proteins are transported by specific imp {alpha} adapters. The different imp {alpha} proteins exhibit substantial sequence divergence and do not appear to be simply redundant in function. Disruption of the IMA10 gene encoding an imp {alpha}-like protein that accumulates in dividing micronuclei results in nuclear division defects and lethality. Thus, nucleus-specific protein import and nuclear function in Tetrahymena are regulated by diverse, specialized karyopherins.

* Corresponding author. Mailing address: Biology Department, Washington University, One Brookings Drive, Campus Box 1137, St. Louis, MO 63130. Phone: (314) 935-8838. Fax: (314) 935-4432. E-mail: dchalker{at}biology2.wustl.edu

{triangledown} Published ahead of print on 1 August 2008.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

{ddagger} Present address: Watson School of Biological Sciences, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724.

Eukaryotic Cell, September 2008, p. 1487-1499, Vol. 7, No. 9
1535-9778/08/$08.00+0     doi:10.1128/EC.00193-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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